Stress his expertise and flaws. (The flaws bring about the internal conflicts)

Highlight his aims and ambitions

Pinpoint the stumbling block, the external conflict

State the cause of the stumbling block. (This is the oppositions)

This Logline below clearly satisfies the points on "how to write a good Logline above.

"A talented but irresponsible teenager schemes to steal his college tuition money when his wealthy father refuses to pay for him to study acting at Juilliard."— Logline for How I Paid for College: A Novel of Sex, Theft, Friendship, and Musical Theater

See the correspondence below:

... "A teenager" (Focusing on the main character)
... "A talented but irresponsible teenager" (Expertise and flaws)
... "to study acting at Juilliard" (Highlighting his aims and ambitions)
... "father refuses to pay for him to study acting" (Pinpointing the stumbling block, the external conflict)
... "his wealthy father" (the cause of the stumbling block)